Many electrical devices are incorporating touchscreen type displays. A touchscreen is a display that detects the presence, location, and pressure of a touch within the display area, generally by a finger, hand, stylus, or other pointing device. The touchscreen enables a user to interact with the display panel directly without requiring any intermediate device, rather than indirectly with a mouse or touchpad. Touchscreens can be implemented in computers or as terminals to access networks. Touchscreens are commonly found in point-of-sale systems, automated teller machines (ATMs), mobile phones, personal digital assistants (PDAs), portable game consoles, satellite navigation devices, and information appliances.
There are a number of types of touchscreen technologies. A capacitive touchscreen panel is coated, partially coated, or patterned with a material that conducts a continuous electrical current across a touch sensor. The touch sensor exhibits a precisely controlled field of stored electrons in both the horizontal and vertical axes to achieve capacitance. The human body is also an electrical device that has stored electrons and therefore also exhibits capacitance. When a reference capacitance of the touch sensor is altered by another capacitance field, such as a finger, electronic circuits located at each corner of the panel measure the resultant distortion in the reference capacitance. The measured information related to the touch event is sent to the controller for mathematical processing. Capacitive sensors can either be touched with a bare finger or with a conductive device being held by a bare hand. Capacitive sensors also work based on proximity, and do not have to be directly touched to be triggered. In most cases, direct contact to a conductive metal surface does not occur and the conductive sensor is separated from the user's body by an insulating glass or plastic layer. Devices with capacitive buttons intended to be touched by a finger can often be triggered by quickly waving the palm of the hand close to the surface without touching.
In capacitive touch applications, the touch sensor acts as an antenna that can pick up ambient noise, such as RF and power supply noise. When used in a touchscreen application, the touch sensors are placed on top of a display screen, such as a liquid crystal display (LCD). Switching noise from the LCD adds significant noise to the touch sensors. When used in an application having an RF transceiver, such as a mobile cell phone, additional noise is picked up by the touch sensors. These noises, if not handled correctly, may cause a capacitive touch screen controller (CTSC) to detect false touches and report wrong touched coordinates.